Solvent Composition is Critical for Carbodiimide Cross-Linking of Hyaluronic Acid as an Ophthalmic Biomaterial

Jui-Yang Lai

doi:10.3390/ma5101986

Abstract

Hyaluronic acid (HA) is one of the most important ophthalmic biomaterials, while also being used for tissue engineering and drug delivery. Although chemical cross-linking is an effective way to improve the material performance, it may as a consequence be detrimental to the living cells/tissues. Given that the cross-linking efficiency is mediated by the solvent composition during the chemical modification, this study aims to explore the stability and biocompatibility of carbodiimide cross-linked HA in relation to material processing conditions by varying the acetone/water volume ratio (from 70:30 to 95:5) at a constant 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) concentration of 100 mM. Our results indicated that after the EDC treatment in the presence of an acetone/water mixture (85:15, v/v), the HA hydrogel membranes have the lowest equilibrium water content, the highest stress at break and the greatest resistance to hyaluronidase digestion. Live/Dead assays and pro-inflammatory cytokine expression analyses showed that the cross-linked HA hydrogel membranes, irrespective of the solvent composition, are compatible with human RPE cell lines without causing toxicity and inflammation. However, it should be noted that the test samples prepared by the cross-linking in the presence of acetone/water mixtures containing 70, 75, and 95 vol % of acetone slightly inhibit the metabolic activity of viable ARPE-19 cultures, probably due to the alteration in the ionic interaction between the medium nutrients and polysaccharide biomaterials. In summary, the water content, mechanical strength and RPE cell proliferative capacity strongly depends on the solvent composition for carbodiimide cross-linking of HA materials.

Highlights

Due to the unique anatomy and physiology of the eye, the development of drug delivery systems for posterior segment ocular diseases remains full of challenges
ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride (EDC) has been reported as a cross-linking agent that is responsible for the intermolecular formation of ester bonds between the hydroxyl and carboxyl groups of Hyaluronic acid (HA) [18]
Our results suggest that the formation of the highest amount of cross-links within the HA hydrogels is observed after the EDC treatment in the presence of acetone/water mixture (85:15, v/v)

Summary

Introduction

Due to the unique anatomy and physiology of the eye, the development of drug delivery systems for posterior segment ocular diseases remains full of challenges. A study from Chang-Lin et al demonstrated that the poly(lactic acid-co-glycolic acid) implants containing dexamethasone, approved by the United States Food and Drug Administration, could be given as a sustained-release formulation for the intravitreal treatment of macular edema after branch or central retinal vein occlusion, and for the treatment of noninfectious uveitis affecting the posterior segment of the eye [2]. Bochot et al reported the potential of liposomes for improving the treatment of cytomegalovirus-induced retinitis in humans by reducing the toxicity and increasing the residence time of several poorly-stable drugs such as peptides and nucleic acids in the eye [4]

Objectives

Results

Conclusion